The present invention relates to techniques for sensing and indicating the fuel reserve in a tank and particularly vehicle fuel tanks containing volatile fuel such as gasoline or mixtures of gasoline and methanol. Where vapor pressure is accumulated in the tank above the liquid fuel level, and particularly at elevated ambient temperature conditions in closed fuel vapor vent systems, the increased vapor pressure can significantly increase the effective density of the fuel. Where a float type sensor is employed for sending a fuel level signal from the tank to a remote indicator for the vehicle operator, the increased buoyancy, without any change in the liquid level of the fuel in the tank, can result in an increased buoyancy force on the float raising the float and thus providing an erroneous liquid level signal. Furthermore, float type sensors are unique or distinct for different fuel tank configurations, and thus require a variety of sensors in inventory for the various configurations in a manufacturers line of vehicle products, which is quite cumbersome and costly in mass production.
Accordingly, it has been desired to provide a simple, low cost yet effective technique or system for sensing the level of volatile liquid fuel in a fuel tank and particularly a fuel tank employed on a motor vehicle which will provide an accurate indication of the fuel level irrespective of the change in ambient temperature conditions and vapor pressure in the tank. It has further been desired to provide a single design liquid level sensor which can accommodate different fuel tank depth configurations.